1. Field of the Invention
The present invention relates to the manufacture of multidirectional reinforcement textures made essentially of ceramic fibers having a silicon compound base, or the production of composite materials.
2. Prior Art
The manufacture of silicon compound based ceramic fibers from precursors containing silicon is known in the art. The precursors are silicon-based organometallic compounds, especially those belonging to the family of polycarbosilanes. These compounds yield a silicon compound based ceramic material when heat treated at a temperature exceeding 800 degrees Celsius in a controlled atmosphere (nitrogen, argon, vacuum, ammonia gas, . . . ).
Some of the silicon organometallic compounds are spinnable and can hence yield fibers made of a silicon compound based ceramic material. The following description shall only cover the case of fibers made principally of silicon carbide, designated SiC fibers. But the scope of the invention also encompasses silicon compound based fibers other than SiC fibers that are derivable from spinnable silicon organometallic compounds.
A well-known process for the manufacture of SiC fibers comprises the following steps:
preparing a precursor consisting of a polycarbosilane (PCS),
fusing the precursor and spinning fibers,
oxidizing the fibers in air to render them infusible, and
performing a ceramic inducement of the oxidized PCS fibers by pyrolysis at up to approximately 1300 degrees Celcius.
Such a process is described in an article by Y. Hasegawa, M. Iimura and S. Yajima published in "Journal of materials Science" 15 (1920) pp. 720-728.
The manufacture of multidirectional textures usable as reinforcement textures for fiber-based composite materials implies carrying out textile-forming mechanical operations on the fibers, e.g. weaving, layering, carding, needling, etc. To that end the fibers must be able to withstand these textile-forming operations and not have their final mechanical properties deteriorated in the process. Yet, although SiC fibers obtained by the above process have a high mechanical strength, they have only a small breaking strain (less than 2%), and are consequently too fragile to undergo certain textile-forming operations, especially carding or needling.
A similar problem is encountered with carbon fibers used in the manufacture of multidirectional reinforcement textures for composite materials, especially of the carbon-carbon type. A carbon precursor commonly used in the manufacture of carbon fibers is polyacrylonitrile (PAN). The fibers obtained after transformation of PAN by a carbonizing heat treatment are too fragile to be submitted to certain textile-forming operations, especially needling. This is why in the manufacture of carbon fiber multidirectional textures the textile-forming mechanical operations are performed on PAN fibers in the preoxidized state, since in that state the fibers possess sufficient mechanical strength and breaking strain to withstand these operations without damage. The carbonizing heat treatment is then performed on the multidirectional texture made from preoxidized PAN fibers.
The above-described process for carbon fibers cannot be applied to known SiC fibers. Indeed, the precursor fiber (e.g. PCS) has negligible mechanical strength, even after the usual oxidation treatment in air. Hence, none of the above-described stages in the manufacture of SiC fibers yield fibers having all the characteristics required to make them capable of withstanding any type of textile-forming operation.